At this point you will either be provided with a code, or you will
receive an error such as 'The Huawei ID used to apply for the unlock
code has not been used on the device for more than 14 days.' If you get
the error, you will need to use the unofficial method below.

Open a command window on your PC / Mac, which needs to have 'adb' and 'fastboot' installed from the Android SDK.{adb Folder}

Enable USB debugging by tapping the build number in Settings ->
About 5 times, then going back and selecting the option from the
Development menu.

Enable OEM unlock in the Development menu.

Connect your phone to the PC and approve the security prompt on the device screen.